Electrically heated tunnel kiln



Dec. 19, 1950 G. N. JEPPSON 2,534,518

ELECTRICALLY HEATED TUNNEL mm Filed April 1, 1949 5 Sheets-Sheet 1 /-v4:-'raz GEORGE N. LJEPP so/v Hrroervsy Dec. 19, 1950 e. N. JEPPSON smc'mcmx HEATED mm. mm

5 Sheets-Sheet 2 Filed April 1, 1949 lNvErvraz GEORGE N. IJEPRSON Dec. 19, 1950 v s. N. JEPPSON smc mcmv x-mmzn TUNNEL mm 5 Sheets-Sheet 3 Filed April 1, 1949 RN mo -s WW, J N E G R. o E G grromvty Patented Dec. 19, 1950 ELECTRICALLY HEATED TUNNEL KILN George N. Jeppson, Worcester, Mass., assignor to Norton Company, Worcester, Mass., a corporation of Massachusetts Application April 1, 1949, Serial No. 84,898

4 Claims.

The invention relates to tunnel kilns.

One object of the invention is to provide a tunnel kiln of simple and practical construction for the vitrification of grinding wheels and other ware. Another object of the invention is to provide a tunnel kiln of compact construction. An-

other object of the invention is to locate planes of radiant heat close to the ware being vitrified in order to avoid thermal differentials in the ware as it is being heated. Another object of the in vention is to provide a tunnel kiln the moving parts of which have a mass which is actually less than that of the ware to be vitrified, thus securing economy in the heat units supplied to the kiln as compared with the mass of ware vitrified.

Another object of the invention is to provide a tunnel kiln of one or more of the characteristics indicated which can employ ordinary batts or simple rectangular configuration as the sole conveying means for the ware in the tunnel. Another object of the invention is to provide a tunnel kiln employing rectangular batts with plane faces as the sole conveying means for the ware in the kiln, and which kiln is so constructed as to deliver radiant energy directly to the undersides of the batts as well as to the upper sides of the ware. Another object of the invention is to provide a tunnel kiln of some of the characteristics indicated having a tunnel floor made in sections which can readily be removed from the tunnel and replaced when, after a period of use, the fioor is unduly worn in one or more places.

Other objects will be in part obvious or in part pointed out hereinafter.

The invention accordingly consists in the features of construction, combinations of elements and arrangements of parts, all as will be illustratively described herein and the scope of the application of which will be indicated in the following claims. a

In the accompanying drawings illustrating one of many possible embodiments of the mechanical features of this invention,

Figure 1 is a side elevation of a tunnel kiln constructed in accordance with the invention. Figure 2 is a fragmentary side elevation on an enlarged scale of the firing zone of the kiln.

Figure 3 is a cross sectional view on an enlarged scale taken on the 1ine3 3 of Figure 1. Figure 4 is a cross sectional view on the same scale as Figure 3 taken on the line 4-4 of Figure 1.

Figure 5 is a cross sectional view on the same scale as Figures 3 and 4 taken on the line 5-5 01' Figure 2.

Figure 6 is a cross sectional view'on the same scale as Figures 3, 4 and 5 taken on the line 6.6 of Figure 1.

Figure 7 is a side view of one of the batt supporting plates removed from the tunnel.

Figure 8 is a plan view of such batt supporting plate.

Figure 9 is a sectional view taken on the lin 9-9 of Figure 8. r

Figure 10 is a plan view on an enlarged scale of a modified form of batt supporting plate showing a pair of plates.

Figure 11 is a cross sectional view taken on the line lI--|l of Figure 10.

Figure 12 is a plan view on the same scale as Figure 10 of a still further. modification of the batt supporting plate.

Figure 13 is a cross sectional view taken on the line |3l3 of Figure 12 on a still further enlarged scale.

Figure 14 is a plan view on the same scale as Figure 10 of a still further modification of the batt supporting plates.

Figure 15 is a sectional view taken on the line |5--|5 of Figure 14 and on the same scale as Figure 13. I

Figure 16 is a plan view on an enlarged scale of a pair of wheel supporting batts.

Figure 17 is a sectional view taken along either of the lines ll-ll of Figure 16 on an enlarged scale.

Figure 18 is a plan view on the same scale as Figure 16 of a modified form of a wheel supporting batt.

Figure 19 is a sectional view taken on the line |9--i9 of Figure 18 on the same scale as Figure 17.

Referring to Figures 1 to 6 inclusive, the kiln may comprise a rectangular parallelepipedal box 10 made of steel plate and having a top H, a bottom 12, a left side wall l3 and a right side wall [4. Suitably secured as by welding to the side walls l3 and I 4 are legs l5 which also serve to brace and strengthen the box Ill. Between successive legs I 5 secured to the side walls 13 and It as by welding are angle iron braces l8 and lid, the latter extending only part way from the top and bottom as shown.

Likewise the top ll of the kiln is braced with angle iron braces I1 and the bottom I2 01 the kiln is braced with angle iron braces l8. It is convenient to identify portions of the kiln by sections, each section" being the volume of the kiln bounded by the plane of a pair of legs II and the plane of a pair of adjacent angle irons It or its. Thus the kiln of this particular illustrative embodiment is said to have l2 sections, and they should be numbered from the entrance end which is at the left in Figure l to the exit end which is at the right in Figure 1, but this division into sections does not in every case coincide with structural differences of the refractory structure of the kiln in the box it.

Referring now to Figures 3 to 6, resting upon the bottom I2 is a mass 20 of refractory bricks substantially in the shape of a parallelepiped extending from end to end of the box ill. The bricks of this mass 20 as well as the other bricks in the box It may be made of any refractory material of adequate strength and thermal resistance. But I have found that a very satis-- factory material is porous kaolin which makes a light weight brick that is therefore easier to handle, which makes a somewhat soft brick which is therefore easy to out, which is sunlciently refractory to withstand a temperature of more than 1300 C., which has high thermal resistance, and which is relatively inexpensive.

On each side of the mass 20 is a wall of bricks 2! extending from the bottom l2 almost to the top H and extending the length of the box in. Resting on the mass 20 which, with certain exceptions hereinafter pointed out, has a flat top, is a continuous succession of tunnel arch bricks 22, each brick being of wide U-shape configuration in upside down position with a thick top portion as shown. These tunnel arch bricks are, however, found only in sections l, 2 and to l2; the firing zone consists of sections 3 and l and in that zone instead of tunnel arch bricks 22 there are tunnel side bricks 23 which in section have generally the same shape of an L upside down. These tunnel arch bricks 22 and tunnel side bricks 23 partly define the tunnel 25 of the kiln through which the ware 26 such as grinding wheels being vitrified is propelled by the propulsion, preferably intermittent but possibly continuous of batts 21.

Resting on the tunnel arch bricks 22 are parallelepipedal masses 30 of bricks, one mass in sections l and 2 and another mass in sections 5 to l2 inclusive, these masses extending between the walls 2i, and between these masses 30 are parallelepipedal masses 3| of bricks resting on the bricks 23 and extending between the walls 2|. Between the wall 13 and the wall 2| as well as between the wall I4 and the wall 2i is a loose mass of insulating material 35 such as diatoma ceous earth and more of this loose mass of insulating material 35 may be placed on top of the masses 3!! and 3| under the top H.

Resting on top of the mass 20 in the tunnel 25 is a continuous section of batt supporting refractory plates 40 shown in section in Figures 3 to 6 inclusive and also illustrated in Figures 7 to 9 inclusive. These batt supporting refractory plates ll) are preferably made of self-bonded aluminum oxide and theyare thus highly refractory and resistant to wear. They preferably have marginal flanges ll which are placed adjacent the vertical portions of the bricks 22 and 22 and these plates 40 have a width across the tunnel only slightly less than the width of the tunnel, just enough less so that they can be readily slid into position. Between the flanges Al the plates 40 are substantially rectangular parallelepipeds but their top surfaces have rounded edges 42 as shown in Figure 9. Likewise the inside edges of the flanges 4| have pref- I erably rounded vertical edges 43 as shown in Figure 8. Also all of the plates 40 in the firing zone, sections 3 and l, have slots 45, and other plates 40 such as those illustrated in the sections of Figures 3 and 5 may have such slots 45. The rest of the plates lll could be unslotted but it is better to have the plates 40 interchangeable so desirably all of them have the slots It. In this connection it may be observed at this point that old plates 40 can be replaced with new plates to simply by pushing the whole line of plates along the tunnel as with a powerful ram and this operation may shift particular plates from one section to another section so therefore it is advisable to make every plate 40 identical with every other plate 40.

The rounded edges 42 as well as the rounded edges 53 could equally well be beveled edges. Either kind will permit batts 21 to be pushed through the tunnel without being caught by the plates ll. These may be generically referred to as smoothed edges.

Referring now to Figure 3, at the entrance end of the kiln is a flue system made out of sheet metal of a heat resistant kind and comprising a short vertical flue 50 connected to a pair of inclined flues 5| which are connected to vertical flues 52 which are connected to horizontal flues 53 and 54. The flues 55 extend through the upper part of the mass 20 and open into a well 55 under a plate 40. The lines 53 extend through a tunnel arch brick 22 to the sides of the top of the tunnel 25. Access openings 56 extend from the vertical flues 52 through the side walls I! and I4 and are normally covered by metal cover plates 51 desirably made out of the same heat resistant metal.

The short vertical flue 50 is connected to an overhead flue pipe 60 made of sheet metal such as steel which in turn is connected to a chimney 6i. It will thus be seen that hot kiln gases, partly air and partly products of combustion of temporary binder in the wheels 26, ifany, will be drawn from the tunnel 25 through the fiues 53, 52, 5| and 60 and the flue pipe 60 into the chimney 6|. This furthermore provides a draught to draw some air from the firing zone under the pates 40 through the lines 54 and so via the flues 52, 5|, 50 and 60 to the chimney 6|. As will be clearly apparent from Figure l, the entire kiln and therefore the tunnel 25 is on a slight incline and it .will be noted in Figure 1 that the well 55 extends all the way from the flues 54 to the firing zone. This draught created by the chimney 6| not only exhausts products of combustion but also draws fresh air into the preheating zone which is sections 1 and 2 of the kiln, this air coming through a door 62 at the exit end of the kiln having adjustable vents not shown. Furthermore, by drawing air and gases from the firing zone through the preheating zone the latter is thereby heated so as to bring the grinding wheels 26 or other ware gradually up to the firing temperature. Suitable dampers, not shown, may be provided in the chimney 6| to control the draught.

Referring now to Figure 4, it is desirable to provide an adjustable back draught to limit and control the amount of air flowing through the annealing zone, sections 5i2 of the kiln, into th firing zone so that the latter may not be cooled too much. Accordingly the overhead flue pipe ill is a long pipe and extends from the front entrance end of the kiln to section it in the annealing zone and, as shown in Figure 4 taken in connection with Figure 1, it is there connected to pipes 65 which extend from the flue pipe 60 horizontally to the side of the kiln and then turn downwardly and are connected to nearly vertical pipes 66 which run downwardly along the outside of the kiln and are connected to a flue pipe 51 extending horizontally through the steel walls |4, |5, through the insulating material 35, through the walls 2| and through a tunnel arch brick 22 and having an opening 38 extending clear across the top of the tunnel 25. The pipes 66 likewise communicate with a flue pipe 68 extending horizontally through th kiln, passing through the walls I3 and I4, the insulating material 35, the walls 2| and the mass 20 and having an opening extending clear across a well 1| under a plate 40, the well 1| being like the well 55 only being localized. Without further description it will be apparent that the draught caused by the chimney 6| draws some air from the tunnel 25 at section ID in the annealing zone and the amount thereof can be regulated by slide dampers 14 and 15 (Figure 1), there being one of each on each side of the kiln controlling respectively the air flowing through the pipe 61 and the air flowing through the pipe 69.

Referring now to Figures 1, 2 and 5, in the third and fourth sections of the kiln extending between the walls l3 and I4 and also projecting slightly outside of such walls are electrical rod resistors 80 at two levels, one level under the tunnel and through the well 55 and the other level through a vault 8| which is an upward extension of the tunnel 25 in the firing zone between the top portions of the tunnel side bricks 23. The resistors 80 of the upper level or bank extend through refractory sleeves 82 bridging the gap between the walls l3 and 4 and the walls 2|, and they extend through the walls 2| and through the tunnel side bricks 23 as well as through the vault 8 I. The electrical rod resistors 80 of the lower bank or level of rod resistors extend in some cases through similar sleeves 82 and in other cases through refractory access blocks 84 that extend from the side wall l3 to the well 55 on one side of the kiln and from the side wall- H to the well 55 on the other side of the kiln. Hollow rectangular refractory pieces 85 bridge the gaps between the walls l3 and I4 and the walls 2| as shown in Figure 5. These as well as the sleeves 82 are provided so that the resistors 80 or the access blocks 84 may be removed without spilling the insulating material 35. In any case the resistors of the lower bank extend through the walls 2| and through the mass 20 as well as through the well 55.

These electrical rod resistors may be of any suitable type but preferably are made out of recrystallized silicon carbide in a manner now known to the art and have cold ends formed as by impregnating with silicon, the cold ends being all of the resistors except the portions thereof in the vault 8| and in the well 55. That is to say the heat generated by the electrical power is practically all liberated in the vault 8| in the case of the upper bank of rod resistors and in the well 55 in the case of the lower bank of rod resistors very little heat being liberated outside of the vault and the well due to the fact that those portions of the resistors in the bricks 23 or in the mass 20 or outwardly thereof are cold ended, that is to say of low resistivity as compared with those portions of the rods in the vault ill and in the well 55. Electrical power may be delivered to the resistor rods 80 by electrical connections as is well known in the art and the power may be controlled by automatic regulators if desired; such forms no part of my invention.

It will now be seen that the upper bank of rod resistors delivers radiant heat to the top of the ware 26 while the lower bank of rod resistors delivers radiant heat to the bottom of the batt supporting refractory plates 40 and through the slots direct to the batts 21. In this manner the ware 26 is vitrified by heat flowing thereinto from both sides thereof, top and bottom, thus avoiding the setting up of strains during the vitriflcation. The batts 21 are preferably made of bonded silicon carbide refractory material and may be of simple rectangular parallelepipedal shape. Such silicon carbide batts are good conductors of heat and also slide easily upon the self-bonded aluminum oxide plates 40. Since these aluminum oxide plates 40 are not quite such ood heat conductors as the silicon carbide batts 21 the provision of the slots 45 is important since it permits the direct flow of radiant heat units from the lower bank of resistors 80 to the ware 26 and at the same time, owing to the shape of the plates 40, without mechanical interference between the batts 21 and the plates 40. It will be noted that due to the rounded corners 42 and 43 of the plates 40 the batts 21 cannot catch on th edges of the plates 40 as the batts 21 are propelled through the tunnel 25.

One advantage of a tunnel kiln constructed in accordance with this invention is that relatively large in area batts 21 can be used, since they may be made very thin being, as they are, supported all over their areas. Thin batts do not fracture from heat shock nearly as readily as thick batts. Furthermore since the batts 21 are supported over their entire areas they are not nearly so likely to break from thermal shock as if they were marginally supported only. In the manufacture of grinding wheels batt breakage facturing the wheels.

has always been a problem and the cost of batts to support the wheels during vitrification has been a material percentage of the cost of manu- At the same time by providing the slots 45 in the plates 40 I am enabled to achieve rapid heat transfer which is especially important in tunnel kilns of this type. The plates 40 are preferably made of self-bonded aluminum oxide rather than of silicon carbide because self-bonded aluminum oxide lasts longer at high temperatures and under thermal strains and furthermore the wearing of the batts is less with this combination than with either material alone.

The purpose of having access blocks such as the blocks 84 is for obtaining access to the well 55 or other'parts of the tunnel 25 to clean out dust powder, grit, soot, or anything else which becomes lodged therein. The continual sliding of batts 21 on plates 40 produces some abrasion and produces some grit which .goes into the well 55. Referring to Figure 6, I may provide access blocks ,88 extending through hollow rectangular pieces 89 bridging the gap between the wall l4 and a wall 2|, these blocks 88 being refractory and tapered as shown so that they can easily be removed to obtain access to the upper part of the tunnel 25. As shown in Figure 1, there may be a number of these access blocks 88.

The kiln is preferably equipped with a belt conveyor 92 at the entrance end which brings batts 21 having ware 26 one by one or two by two to a position over an elevator 93 having a plunger 34 extending into an hydraulic cylinder 85, and

at intervals 9. ram 96 operated hydraulically by a cylinder 91 rams a batt or a pair of them into the tunnel 25 and whenever this is done, assuming the tunnel 25 is full of batts, one or two batts 21 emerge from the exit end of the kiln and are removed by a conveyor 98. The door 62 at the exit end of the kiln as well as a door at the entrance end of the kiln is automatically operated to open the tunnel 25 whenever the batts are rammed. This mechanism however need not be further detailed herein since any feeding, conveying and ramming mechanism may be used, and a feeding, conveying, ramming and discharging mechanism along the lines above described is fully disclosed in my copending application with Edward Van der Pyl, Serial N 0. 73,312, filed January 28, 1949.

Referring now to Figures and 11, batt supporting plates 40a of slightly modified form are shown. These plates have slots 45a which extend across the tunnel 25 instead of along the line of the tunnel 25. This modification has some advantages in that the plates are stronger in cross bending, that is to say it will take a heavier load to break them. Furthermore the plate 40 is completely broken if two marginal portions on either side of a slot 45 are broken while a plate 40a is not completely broken unless four portions between and outside of the slots 45a are broken. Another feature of the plates 40a is that they have interlocking tongues IOI and grooves I02 so that if one plate 40a is broken the adjacent plates 40a will uphold it. All corners and edges of the plates 40a. which are contacted by the batts 21 are smoothed.

Figures 12 and 13 show still another modification of the batt supporting plates.- These batt supporting plates 40b of Figure 13 have holes 45b therein for the passage of heat. Again all corners and edges which contact the batts 21 are smoothed as shown. Preferably the plates 40b rod resistors 00 to the batts 21 they serve to protect the plates against heat shock. That is to say, there is a chance for differential thermal expansion between various portions of the plates due to these foramina. The least likely of all the plates to suffer from thermal shock are the narrow plates 400 of Figures 14 and 15. But if any of them should break, they will be supported by adjacent plates due to the tongues and grooves.

The batts 21 are better illustrated in Figures 16 and 17. They are rectangular parallelepipeds preferably about square but they have rounded or otherwise smoothed corners I03 and rounded or otherwise smoothed underside edges I04. These smoothed corners and edges further assist in preventing a jam in the tunnel, since due to all the rounded or smoothed corners and edges there is practically no chance of a batt mechanically interlocking with any plate. I prefer that the edges of the batts 21 be plane as thereby the thrust is carried from one plate to another plate with little danger of any resultant force at an angle to the batts or plates. Should a, batt 2l fracture, it will still go through the tunnel since it will be supported by the plates 40, 40a, 40b or 40c.

Figures 18 and 19 show slightly modified batts 21a with parallel grooves I05 on the underside leaving downwardly projecting skid portions I00 therebetween and outside thereof. The portions I01 of these batts 21a can be a little thinner than the batts 21 and this helps to reduce thermal shock on the batts while at the same time they slide Just as easily through the kiln. The skid portions I06 should extend in the direction of the tunnel rather than across the tunnel.

It will thus be seen that there has been provided by this invention a tunnel kiln in which the various objects hereinabove set forth together with many thoroughly practical advantages are successfully achieved. As many possible embodiments may be made of the above invention and as many changes might be made in the embodiment above set forth, it is to be understood that all matter hereinbefore set forth or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense.

I claim:

, 1. In a tunnel kiln, a refractory structure forming an elongated tunnel, said tunnel having a firing zone constructed to have a vault and a well, an upper bank of substantially horizontal and parallel electrical rod resistors extending from side to side of and through said refractory structure and through said vault, a lower bank of substantially horizontal and parallel electrical rod resistors belowsaid first bank extending from side to side of and through said refractory structure and through said well, said tunnel being further formed and shaped to have ledges which are substantially horizontal in the transverse direction one on either side of and above said well and bounding said well on the to thereof, a plurality of rectangular refractory plates in continuous contiguous relation in said tunnel spanning said well and resting on said ledges and extending from side to side of said tunnel and, in the firing zone, having foramina therein for the passage of radiant energy therethrough, and flat rectangular refractory batts also in continuous contiguous relation in said tunnel supported by said plates, there being a clear space between the bottom of the plates and the lower bank of electrical rod resistors in said well.

2. In a tunnel kiln as claimed in claim 1, the combination with the parts and features therein specified, of the further feature that the refractory plates are made of aluminum oxide and the batts are made of silicon carbide.

3. In a tunnel kiln as claimed in claim 2, the combination with the parts and features therein specified, of the further feature that the refractory plates have tongues on one edge and are grooved on the opposite edge and are interlocked thereby.

4. In a tunnel kiln as claimed in claim 1, the combination with the parts and features therein specified, of the further feature that the refractory plates have tongues on one edge and are grooved on the opposite edge and are interlocked together thereby.

GEORGE N. JEPPSON.

(References on following page) 10 REFERENCES CITED Number Name Date The followin references are of record in the' 11564319 Lee 1923 m of this paint: 1,799,980 Hartford Apr. 7, 1931 1,875,365 Begeman Sept. 6, 1932 UNITED STATES PATENTS 5 2,034,721 Howe Mar. 24, 1936 Number Name Date 2,320,172 Brooke et a1 May 25, 1943 670,777 Guastavino Mar. 26, 1901 2,404,059 Hall July 16, 1946 671,990 Diescher Apr. 16, 1901 2,465,137 Van Nordstrand Mar. 22, 1949 732,545 Graham June 30, 1903 1,567,143 Hay Dec. 29, 1925 10 FOREIGN PATENTS 1,579,258 Strommer Apr. 6, 1926 Number Country Date 1,628,273 Richardson May 10, 1927 570,113 Great Britain June 22, 1945 

